1. Field of the Invention
The present invention relates to a process for the separation of cerium and rare earth values contained in an aqueous phase thereof, and particularly relates to the separation of cerium from other rare earth (RE) values, said elements comprising an aqueous solution thereof, notably a nitric solution.
2. Description of the Prior Art
Rare earth metals are typically found associated in various minerals such as monazite, bastnaesite or xenotime, for example. One means for separating the different rare earth values from each other consists of carrying out successive liquid/liquid extractions of solutions of salts of said rare earths.
Processes are already known to this art which enable such a separation. See, for example, U. S. Pat. No. 2,564,241. Typically, these processes are based on the selective extraction of cerium (IV) with respect to RE (III) when using certain organic solvents, such as tributylphosphate. Thus, an aqueous phase containing cerium (IV) and RE (III) is contacted with a solvent of the aforementioned type which selectively extracts the cerium, while the RE (III) remains in the aqueous raffinate. To subsequently extract the cerium from such organic solvent, it is converted into oxidation state (III) by chemical reaction and the organic phase is next extracted with an aqueous phase, wherefrom the cerium values are recovered.
Although such prior art processes enable the efficient separation of cerium, they are not without disadvantage. In effect, the use of a chemical reducing agent necessarily entails the introduction of extraneous impurities, particularly in the form of foreign organic or metallic species. In addition, extrinsic reagents are consumed over the course of the operation. Also, it is frequently necessary to utilize rather exotic apparatus.